Pain and dysfunction associated with the temporomandibular joint (TMJ) and the muscles of mastication have produced conflicting etiological theories and diverse treatment modalities. The controversy may be due in part to the lack of either observable pathology or definitive diagnostic signs. The electromyographic silent period may provide such a sign and perhaps some insight into the etiology. The silent period is a brief pause in the electrical activity of a muscle in the midst of an otherwise sustained, voluntary contraction. The mean duration of the silent period is greater in a group of TMJ dysfunction patients than in a group of asymptomatic subjects. The purpose of our research is to investigate both the clinical utility of the electromyograhic silent period and the basic mechanisms underlying its generation. Current results suggest that level of voluntary activity is not a determining factor in jaw muscle silent period duration although it is in limb muscles, that silent period duration increases with increased symptom severity, and that dental interventions such as immediate complete dentures and rapid palatal expansion can cause a significant increase in silent period duration.